Known processes for image formation by electrophotography include a process wherein a toner image is recorded on an electrophotographic photoreceptor and then transferred to ordinary paper, a process in which an image is directly formed on a recording material comprising a support, such as paper and films, having provided thereon an electrophotographic photoreceptor, and the like. Materials that have been employed for the electrophotographic photoreceptors include inorganic materials, e.g., selenium, cadmium sulfide, zinc oxide, and the like. With the recent development of organic electrophotographic photoreceptors, such as those comprising poly-N-vinylcarbazole and 2,4,7-trinitrofluoren-9-one as disclosed in U.S. Pat. No. 3,484,237; those prepared by sensitizing poly-N-vinylcarbazole with pyrylium salt dyes as disclosed in U.S. Pat. No. 3,617,268 corresponding to Japanese Patent Publication No. 25658/73; those consisting mainly of organic pigments as disclosed in U.S. Pat. No. 3,898,084 corresponding to Japanese Patent Application (OPI) No. 37543/72 (the term "OPI" as used herein means "unexamined published application"); those consisting mainly of eutectic complexes composed of dyes and resins as disclosed in U.S. Pat. Nos. 3,732,180 and 3,684,502 which correspond to Japanese Patent Application (OPI) No. 10785/72; and the like, it has become easy to produce photoreceptors by coating organic photoconductive materials as such or as a mixture with an appropriate binder on a support.
Furthermore, it has also become possible to produce light-transmitting electrophotographic recording materials by properly selecting the organic photoconductive materials and the supports (see Optical Eng., Vol. 20, No. 3, 365 (1981)).
Compared with the commonly employed silver halide photographic recording materials, electrophotographic recording materials have their own advantages. For example, since the electrophotographic recording materials are not photosensitive until they are subjected to electrostatic charging, production and finishing thereof are easy; packaging therefor may be simple; and processings such as development can easily be carried out.
Electrophotography is further characterized in that exposure and development can repeatedly be effected on the same recording material. In other words, a silver halide recording material once having formed thereon an image by development processing cannot be used any more for recording another image. Whereas, according to electrophotography, images can be recorded on optional areas of the same recording material whenever desired.
On the other hand, in electrophotographic recording materials, particularly lengthwise long ones, a conductive material may fall off while being carried during charging, exposure and development and attach to unexposed areas or an exposed photosensitive layer surface which has been electrostatically charged to thereby leak a part of the electric charge, resulting in electrostatic contamination of an image, which appears as image noise.
Furthermore, when a lengthwise long electrophotographic photoreceptor prepared by using the recording material as described in Research Disclosure, Vol. 109, 61, "Electrophotographic Element, Materials and Processes" (May, 1973) is repeatedly used, friction between an image-recording surface and a back surface causes fall-off of the image or scratches on the image-recorded surface or back surface.
Furthermore, lengthwise long electrophotographic recording materials involve disadvantages such as deterioration of the driving property of cameras, projectors or reading apparatus and causing film chips.
In order to overcome the above-described disadvantages associated with electrophotographic recording materials, improvement of slipping property by reducing the friction coefficient of the recording materials has been considered. However, proposals in this direction have scarcely been made in the field of electrophotographic recording materials. To the contrary, a variety of techniques have been disclosed to this effect in the field of silver halide recording materials.
Examples of known techniques for improving the slipping property of silver halide recording materials include a method of adding a certain kind of gelatin hardener to a photographic constituting layer to heighten the strength against scratches, as described in British Pat. No. 1,270,578; a method of simultaneously adding dimethyl silicon and a specific surfactant to a photographic emulsion layer or a protective layer thereby to impart the slipping property to the layer, as described in U.S. Pat. No. 3,042,522; a method comprising coating a mixture of dimethyl silicon and diphenyl silicon on a back surface of a photographic film base thereby to impart the slipping property, as described in U.S. Pat. No. 3,080,317; a method comprising incorporating triphenyl terminal-blocked methylphenyl silicone in a protective layer to impart the slipping property to the photographic film, as described in British Pat. No. 1,143,118; and a method for preventing the uppermost layer from disadvantageous adhesion to different substances due to contact, which comprises dispersing spherical particles of the so-called matting agent, such as inorganic compounds (e.g., silver halide, silica, stronitium barium sulfate, etc.) and high polymers (e.g., polymethyl methacrylate latex, etc.), in a surface layer of a light-sensitive material thereby forming a matted dry film.
Application of such backing layers according to these known techniques proposed for silver halide recording materials to the electrophotographic films was thought to surely bring about considerable improvement of running durability of the films with less susceptibility to scrathes during running on either a photosensitive surface or a backing surface.
However, such techniques turned out to adversely affect the electrophotographic characteristics except in some special cases. More specifically, with an elapse of time under normal humidity or high humidity, a part of the composition of the backing layer is transferred to the photosensitive layer, resulting in suppression of surface charging, reduction of sensitivity, increase of a residual potential, unevenness of image formation, and the like.